As per our conversation in the CB,

use strict;
use warnings;

open(my $sav_fh, '<', 'saved_system.txt'  ) or die;
open(my $cur_fh, '<', 'current_system.txt') or die;

my @sav_files = sort <$sav_fh>;
my @cur_files = sort <$cur_fh>;

my @rem_files;
my @new_files;

while (@sav_files && @cur_files) {
    if ($sav_files[0] lt $cur_file[0]) {
        push @rem_files, shift(@sav_files);
    }
    elsif ($sav_files[0] gt $cur_file[0]) {
        push @new_files, shift(@cur_files);
    }
    else {
        shift @sav_files;
        shift @cur_files;
    }
}

push @rem_files, @sav_files;
push @new_files, @cur_files;

open(my $rem_fh, '>', 'removed.txt') or die;
print $rem_fh @rem_files;
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If you want just know there was a change, go with File::Compare mentioned above.

I think you probably need to know what files were added and removed, in other word difference between your file list. You can try following approach:

First make sure your lists in files are sorted. Then use Text::Diff module like this:

use Text::Diff;

my $diff = diff "saved_system.txt", "current_system.txt", { STYLE => "
+OldStyle" };

my (@added,@removed);
for(split /\n/,$diff) {
    next if /^\d/;     # skip line numbers
    push @added,$1   if /^> (.*)$/;
    push @removed,$1 if /^< (.*)$/;
}

print "Added files:\n";
for my $file (@added) {
    print $file,"\n";
}

print "\nRemoved files:\n";
for my $file (@removed) {
    print $file,"\n";
}
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It prints output to console, but it is easy to change for printing into file.

-- hope this helps, Roman

It seems to me that will fail if saved_system.txt and current_system.txt are ordered differently.

Agree completely, thats why I pointed that lists have to be sorted. Since this seems to be followup to storing all file info, I assumed that no problem make lists sorted on its creation.

On any case, your solution below seems to be more elegant and independent on libraries.

-- Roman

use strict;
use warnings;
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Another advice is to use the three argument form of open and show the open modes your files are accessed under (input, output, appending, piping...),

open (FH, '<', "saved_system.txt");
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open(FH, '<', 'saved_system.txt')or die("Couldn't open file, $!");
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Update:ikegami posted a wholesome example while I was writing these ideas :)...

Also use File::Compare;